The present invention relates to a soaking apparatus for soaking materials to be treated by heating.
Conventionally, a heat treatment furnace for treating a material to be treated in the furnace at a uniform temperature has a heat source such as a burning gas and an electric heater. While an atmosphere in the furnace is stirred with a circulation fan in order to uniformize a temperature in the furnace, a temperature at a certain point in the furnace which represents the temperature in the furnace is measured, and an operation of a heat source heating the inside of the furnace as well as the circulating fan is controlled so that the temperature at the representative point is maintained at a predetermined value.
An example of a material to be treated which requires soaking is an electronic device substrate. An electronic device substrate is made of one of glass, ceramics and plastic, or comprises a base made of one of glass, ceramics and plastic with a layer of one of metal, an inorganic material and an organic material formed on a surface of the base, which add desired functions on the base surface, respectively. An electronic device substrate subjected to a heat treatment has no differences in quality with a desired accuracy in the dimension. In these days functional layers formed on substrate surfaces have more minute pattern spaces, which increasingly require a uniformity of a layer of higher accuracy. In addition, as dimensions of screens of display devices become larger, an electronic device substrate having a larger dimension over 1000 mmxc3x971000 mm is needed.
Furthermore, in case of an electronic device substrate, particles such as dust in an atmosphere in a heat treatment furnace, adhearing to a substrate surface during a heat treatment step, lead to undesirable quality. Therefore, an atmosphere in a furnace requires a high degree of cleanliness. As a method to enhance the cleanliness, a gas such as nitrogen or air which has been heated by a heat source such as a gas or an electric heater outside a heat treatment furnace is filtrated with a heat-resistant particle collection filter, and then fed into the furnace. Since the gas or air fed to the heat treatment furnace is of a high temperature, a heat-resistant particle collection filter made of glass fibers or organic fibers is used.
According to the above-described conventional heat treatment method, the temperature of the atmosphere in the heat treatment furnace is only controlled at a representative point and is not controlled at other points. Thus, the overall furnace does not have a uniform temperature, making it difficult to treat materials having large surfaces at a uniform temperature.
As the conventional method is to control soaking of a material to be heated during a temperature holding period, it is also difficult to control rates of temperature rising and temperature falling during a temperature rising period and a temperature falling period before and after the temperature holding period.
When treating a large-sized electronic device substrate, the temperature in a heat treatment furnace cannot be raised with respect to each area individually, leading to a non-uniform temperature in the furnace. Therefore, it is difficult to provide an electronic device substrate having a layer of uniform quality.
At a high temperature of over 300xc2x0 C., the durability of a heat-resistant particle collection filter deteriorates, and the filter generates particles by itself, thereby degrading cleanliness inside a heat treatment furnace. Additionally, in this case, a circulation fan is used to stir an atmosphere in the furnace to uniformize the temperature in the furnace. Then, a substrate shakes or vibrates to generate dust by crushing or wearing, which causes new particles to scatter in the furnace. Thus, it is no longer possible to maintain cleanliness inside the furnace.
As described above, the conventional methods involve a variety of problems.
An object of the present invention is to provide a soaking apparatus used for treating a material which requires a higher degree of accuracy in soaking as well as greater cleanliness.
In order to accomplish the above object, a soaking apparatus according to the present invention is a heat treatment apparatus for soaking a material to be treated comprising a heat treatment furnace having walls, a ceiling and a floor, each surface of said walls, said ceiling and said floor being divided into a plurality of sections, at least one heater block mounted on each of said sections, a thermal sensor provided to said heater block, and a thermal controller to control heating of the heater block based on a temperature measured by the thermal sensor.
The heat treatment furnace of the above soaking apparatus is a batch type furnace. Preferably, a part of the walls of the furnace is provided with a door member which opens when a material to be treated is inserted and removed. The furnace can treat materials both in a plate-like form and in a solid form.
As the heater block, a plate-like form electric heater or a ceramic infrared heater may be used, for example. It is preferable to employ heaters which generate as few particles as possible.
As the heater block is mounted on each surface of the walls, ceiling and floor, respectively, it is possible to radiate heat from a predetermined position in a predetermined direction, thereby raising a temperature of a material up to a predetermined value as well as maintaining the temperature.
Furthermore, a soaking apparatus according to the present invention is a heat treatment apparatus for soaking a material to be treated comprising a heat treatment furnace having walls, a ceiling and a floor, each surface of said walls except for the walls on side of an inlet and an outlet of the furnace, said ceiling and said floor being divided into a plurality of sections, at least one heater block mounted on each of said sections, a thermal sensor provided to said heater block, a thermal controller to control heating of the heater block based on a temperature measured by the thermal sensor, and a conveyor disposed in the heat treatment furnace to carry the material to be treated from the inlet of the furnace to the outlet of the furnace.
The heat treatment furnace of the above soaking apparatus is a continuous type furnace, in which a material to be treated is carried from the inlet of the furnace to the outlet of the furnace by the conveyor. The material can be passed through a space surrounded by the heater blocks, each of which has been heated to a predetermined temperature, which enables a uniform temperature of the material to be easily controlled.
Whether the heat treatment furnace is the batch type or the continuous type, a cooling device to cool down the walls, the ceiling and the floor of the furnace may be preferably provided on outer surfaces of the walls, the ceiling and the floor on opposite sides to surfaces on which the block heater is mounted.
The temperature in the heat treatment furnace rises up to 300xc2x0 C. or more, which, however, is not high enough to melt down the walls, ceiling and floor. Therefore, it is not necessary to consistently operate the cooling device. Nevertheless, the temperature, when becoming extremely high by the heater blocks, can be readily lowered to an appropriate level by the cooling device. In addition, after a temperature has been raised and held by the block heaters, a temperature falling rate can be controlled.
Preferably, a heat-resistant glass to separate areas on which the heater block is mounted from a space inside the heat treatment furnace may be provided in front of the heater blocks on a side facing to the center of the furnace.
With the heat-resistant glass for separating the areas, dust, if generated from the heater blocks, cannot enter the space inside the furnace and does not affect a material to be treated, improving cleanliness of an atmosphere inside the furnace.
Preferably, the material to be treated may be a substrate made of one of glass, ceramics and plastic, or comprises a base made of one of glass, ceramics and plastic with a layer made of one of metal, an inorganic material and an organic material formed on a surface of the base. Furthermore, a cassette to hold a plurality of materials to be arranged in parallel to each other may be detachably mounted in the heat treatment furnace.
Plate-like materials to be treated may be arranged in a vertical or horizontal position. Each of the heater blocks may have an elongated form, for example, to be disposed in parallel to or vertical to the materials.
When plate-like materials to be treated are carried by a conveyor, the cassette may preferably be disposed so that a normal line to the materials are in parallel to a moving direction of the conveyor.
By the above structures, a large amount of materials can be treated at one time, and the heater blocks accurately control the temperature.